[ovs-dev] userspace datapath performance (was: Re: Threaded userspace datapath)

[Ben Pfaff]

More than anything I'd like to see an analysis, based on at least
simple measurements, probably including some conjecture, of the reason
or reasons that the threaded datapath yields performance that is so
much better.  If it comes down to something not fundamental to having
threads, then we can talk about the trade-offs between working on
those issues directly versus introducing threading.

One issue that's been brought up is the fact that Open vSwitch throws
away the information provided by "poll" regarding the file descriptors
that are ready for read or write.  If that's a significant cost that
contributes to slowness (I'm not convinced yet, but I could be
convinced by measurements), then that's something that we can work on;
I'm happy to do that.  I think that we can work on that without
completely changing how the poll loop works.

I don't remember other proposed reasons why the userspace datapath is
slow.